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Abstract
Mean and fluctuating winds wore measured within the atmospheric surface layer at three locations across Long Island during the landfall of Hurricane Belle on 9 August 19176. An order of magnitude increase in wind shear was observed. A maximum friction velocity of ∼133 cm s−1 and a maximum energy dissipation rate of ∼130 cm−2 s−3 were estimated. Mean wind speeds at the beach were found to he 3–5 times the corresponding wind speeds inland. A periodicity in rainfall associated with bands of thundershowers was observed. A storm surge of ∼125 cm was estimated from water level records near Shinnecock Inlet. The records indicated the three successive stages, forerunner, hurricane surge and resurgence, associated with the hurricane.
Abstract
Mean and fluctuating winds wore measured within the atmospheric surface layer at three locations across Long Island during the landfall of Hurricane Belle on 9 August 19176. An order of magnitude increase in wind shear was observed. A maximum friction velocity of ∼133 cm s−1 and a maximum energy dissipation rate of ∼130 cm−2 s−3 were estimated. Mean wind speeds at the beach were found to he 3–5 times the corresponding wind speeds inland. A periodicity in rainfall associated with bands of thundershowers was observed. A storm surge of ∼125 cm was estimated from water level records near Shinnecock Inlet. The records indicated the three successive stages, forerunner, hurricane surge and resurgence, associated with the hurricane.
Abstract
A simple empirical model is developed based on physical and dimensional considerations to predict the height of air mass modification due to a change in surface characteristics. Most of the input parameters can be obtained from surface weather maps. The results of the empirical model are found to be in good agreement with observations made in the atmosphere over ocean with cooler downwind temperatures. The model is then used with appropriate parameters to predict flow modification over a heated surface in a wind tunnel for different upwind and downwind surface conditions.
Abstract
A simple empirical model is developed based on physical and dimensional considerations to predict the height of air mass modification due to a change in surface characteristics. Most of the input parameters can be obtained from surface weather maps. The results of the empirical model are found to be in good agreement with observations made in the atmosphere over ocean with cooler downwind temperatures. The model is then used with appropriate parameters to predict flow modification over a heated surface in a wind tunnel for different upwind and downwind surface conditions.
Abstract
Turbulence fluctuations over water are found to change for wind speeds more than 10–12 m s−1. Increase in turbulence level beyond this critical wind speed may be attributed to the formation of helical roll vortices. Integral scales of turbulence estimated over water are found to be several times larger than corresponding values over land.
Abstract
Turbulence fluctuations over water are found to change for wind speeds more than 10–12 m s−1. Increase in turbulence level beyond this critical wind speed may be attributed to the formation of helical roll vortices. Integral scales of turbulence estimated over water are found to be several times larger than corresponding values over land.
Abstract
Chi-square goodness-of-fit is used to test the hypothesis that the medium scale of turbulence in the atmospheric surface layer is normally distributed. Coefficients of skewness and excess are computed from the data. If the data are not normal, these coefficients are used in Edgeworth's asymptotic expansion of Gram-Charlier series to determine an alternate probability density function. The observed data are then compared with the modified probability densities and the new chi-square values computed.
Seventy percent of the data analyzed was either normal or approximately normal. The coefficient of skewness g 1 has a good correlation with the chi-square values. Events with |g 1| < 0.21 were normal to begin with and those with 0.21 < |g 1| < 0.43 were approximately normal. Intermittency associated with the formation and breaking of internal gravity waves in surface-based inversions over water is thought to be the reason for the non-normality.
Abstract
Chi-square goodness-of-fit is used to test the hypothesis that the medium scale of turbulence in the atmospheric surface layer is normally distributed. Coefficients of skewness and excess are computed from the data. If the data are not normal, these coefficients are used in Edgeworth's asymptotic expansion of Gram-Charlier series to determine an alternate probability density function. The observed data are then compared with the modified probability densities and the new chi-square values computed.
Seventy percent of the data analyzed was either normal or approximately normal. The coefficient of skewness g 1 has a good correlation with the chi-square values. Events with |g 1| < 0.21 were normal to begin with and those with 0.21 < |g 1| < 0.43 were approximately normal. Intermittency associated with the formation and breaking of internal gravity waves in surface-based inversions over water is thought to be the reason for the non-normality.
Abstract
Observations of mean wind speed and longitudinal turbulence at a height of 8 m over the Atlantic ocean, 5 km off Long Island, New York, were compared with simultaneous observations at the beach. Results were grouped into wind direction classes characteristic of changes in roughness and fetch. Mean winds over the ocean were 15–100% higher than those at the beach. Changes in turbulence seem to depend on variations in the aerodynamic roughness of the sea surface and the thermal processes that take place over the water. A decrease in turbulence over the ocean relative to that at the beach due to a decrease in sea surface roughness for alongshore flows could be predicted reasonably well with a simple logarithmic wind profile relationship.
Abstract
Observations of mean wind speed and longitudinal turbulence at a height of 8 m over the Atlantic ocean, 5 km off Long Island, New York, were compared with simultaneous observations at the beach. Results were grouped into wind direction classes characteristic of changes in roughness and fetch. Mean winds over the ocean were 15–100% higher than those at the beach. Changes in turbulence seem to depend on variations in the aerodynamic roughness of the sea surface and the thermal processes that take place over the water. A decrease in turbulence over the ocean relative to that at the beach due to a decrease in sea surface roughness for alongshore flows could be predicted reasonably well with a simple logarithmic wind profile relationship.
Abstract
A three-dimensional hot-film probe, a Vector Vane, and an Aerovane were used to measure the mean wind speed and turbulence structure in the atmospheric surface layer at a location on the south shore of Long Island. A comparison was recently made of the characteristics of the three instruments to determine their capabilities in measuring the various meteorological parameters of interest. Results from the comparison indicated that the mean wind speed measured by the three instruments was the same.
The estimated spectral densities of the Vector Vane were approximately equal to those of the hot-film probe to a cyclic frequency of 1 Hz. The standard deviations of the velocity fluctuations were equal.
Comparison of the longitudinal velocity fluctuations measured by the Aerovane and Vector Vane were not significantly different to a frequency of 0.3 Hz. The Aerovane underestimated the lateral velocity fluctuations.
Abstract
A three-dimensional hot-film probe, a Vector Vane, and an Aerovane were used to measure the mean wind speed and turbulence structure in the atmospheric surface layer at a location on the south shore of Long Island. A comparison was recently made of the characteristics of the three instruments to determine their capabilities in measuring the various meteorological parameters of interest. Results from the comparison indicated that the mean wind speed measured by the three instruments was the same.
The estimated spectral densities of the Vector Vane were approximately equal to those of the hot-film probe to a cyclic frequency of 1 Hz. The standard deviations of the velocity fluctuations were equal.
Comparison of the longitudinal velocity fluctuations measured by the Aerovane and Vector Vane were not significantly different to a frequency of 0.3 Hz. The Aerovane underestimated the lateral velocity fluctuations.
Abstract
A research program is in progress at Brookhaven National Laboratory to determine the nature of atmospheric diffusion from a representative oceanic site, to relate observed diffusion patterns to meteorological and oceanographic variables, and to develop models to describe such diffusion. The program was initiated in response to plans for construction of offshore nuclear power plants.
Tracer experiments are conducted utilizing oil-fog smoke released from a boat stationed from 1–3 mi off-shore during onshore flows. The smoke is photographed from above and from the side to document lateral and vertical spread. The crosswind concentration distribution is measured by vehicle- and boat-mounted densitometers during successive traverses across the plume. Wind, turbulence and temperature at several levels are measured on the beach by tower-mounted instruments. Temperature profiles at greater heights are measured by kytoon- and aircraft-borne sensors. Water temperatures are also measured. Winds aloft are determined by pibal ascents and turbulence at various altitudes is sampled by an aircraft-mounted variometer.
Preliminary results show that diffusion is governed primarily by water and air temperature differences. With colder water, low-level air is very stable and diffusion minimal but water warmer than the air induces vigorous diffusion. Measurements of plume width and height have been obtained which are smaller and of normalized concentration which are larger than those predicted for the Pasquill F category. Measured values of plume width can be predicted from Eulerian measurements at the beach.
Abstract
A research program is in progress at Brookhaven National Laboratory to determine the nature of atmospheric diffusion from a representative oceanic site, to relate observed diffusion patterns to meteorological and oceanographic variables, and to develop models to describe such diffusion. The program was initiated in response to plans for construction of offshore nuclear power plants.
Tracer experiments are conducted utilizing oil-fog smoke released from a boat stationed from 1–3 mi off-shore during onshore flows. The smoke is photographed from above and from the side to document lateral and vertical spread. The crosswind concentration distribution is measured by vehicle- and boat-mounted densitometers during successive traverses across the plume. Wind, turbulence and temperature at several levels are measured on the beach by tower-mounted instruments. Temperature profiles at greater heights are measured by kytoon- and aircraft-borne sensors. Water temperatures are also measured. Winds aloft are determined by pibal ascents and turbulence at various altitudes is sampled by an aircraft-mounted variometer.
Preliminary results show that diffusion is governed primarily by water and air temperature differences. With colder water, low-level air is very stable and diffusion minimal but water warmer than the air induces vigorous diffusion. Measurements of plume width and height have been obtained which are smaller and of normalized concentration which are larger than those predicted for the Pasquill F category. Measured values of plume width can be predicted from Eulerian measurements at the beach.
Abstract
Experiments were conducted to investigate the differences in diffusion from an obstacle to free air flow in the ocean and from an undisturbed ocean site. A small island was used as the obstacle and simultaneous releases of oil-fog smoke were made from the island and from a nearby boat. The widths of the plumes and their concentration distributions were measured quantitatively during traverses across the plumes by a second boat. Extensive series of photographs were taken of the plumes from the surface and from the air. Meteorological measurements were made at two locations on the island, from the boats and from an aircraft. One test series was conducted during unstable conditions and a second series with neutral and stable conditions.
Width of the island plume over short periods was from 1.5 to 4 times that of the boat plume with the greatest difference during stable periods. Over longer periods, the differences were somewhat greater and much of the dispersion was caused by plume meander. Height of the island plume averaged about twice that of the boat plume. Normalized maximum centerline concentrations from the boat plume were 1.4 times those of the island plume during unstable periods but about twice during stable and neutral conditions. Averaged over all tests, dispersion from the island was about twice as great as from the boat.
Abstract
Experiments were conducted to investigate the differences in diffusion from an obstacle to free air flow in the ocean and from an undisturbed ocean site. A small island was used as the obstacle and simultaneous releases of oil-fog smoke were made from the island and from a nearby boat. The widths of the plumes and their concentration distributions were measured quantitatively during traverses across the plumes by a second boat. Extensive series of photographs were taken of the plumes from the surface and from the air. Meteorological measurements were made at two locations on the island, from the boats and from an aircraft. One test series was conducted during unstable conditions and a second series with neutral and stable conditions.
Width of the island plume over short periods was from 1.5 to 4 times that of the boat plume with the greatest difference during stable periods. Over longer periods, the differences were somewhat greater and much of the dispersion was caused by plume meander. Height of the island plume averaged about twice that of the boat plume. Normalized maximum centerline concentrations from the boat plume were 1.4 times those of the island plume during unstable periods but about twice during stable and neutral conditions. Averaged over all tests, dispersion from the island was about twice as great as from the boat.
Abstract
Thermal structure of the marine boundary layer (MBL) was studied during a five-day cruise over the coastal Atlantic Ocean off North Carolina. Three different synoptic conditions were present: ahead of a low moving along the coast, in the area of a frontal zone and during a cold air outbreak. The marine boundary layer height was deeper (approximately 1500 m) and more sharply defined during the cold air outbreak than when the flow was southwesterly with a long fetch over water; the height was only about 1000 m for the latter case. Latent heat fluxes were significantly larger than sensible heat, but during the cold air outbreak, sensible heat fluxes increased appreciably.
Abstract
Thermal structure of the marine boundary layer (MBL) was studied during a five-day cruise over the coastal Atlantic Ocean off North Carolina. Three different synoptic conditions were present: ahead of a low moving along the coast, in the area of a frontal zone and during a cold air outbreak. The marine boundary layer height was deeper (approximately 1500 m) and more sharply defined during the cold air outbreak than when the flow was southwesterly with a long fetch over water; the height was only about 1000 m for the latter case. Latent heat fluxes were significantly larger than sensible heat, but during the cold air outbreak, sensible heat fluxes increased appreciably.
